1. Field of the Invention
The present invention relates to a method used in a wireless communication system and related communication device, and more particularly, to a method of handling a network entry in a cell cluster and related communication device.
2. Description of the Prior Art
A long-term evolution (LTE) system supporting the 3rd Generation Partnership Project (3GPP) Rel-8 standard and/or the 3GPP Rel-9 standard are developed by the 3GPP as a successor of a universal mobile telecommunications system (UMTS), for further enhancing performance of the UMTS to satisfy increasing needs of users. The LTE system includes a new radio interface and a new radio network architecture that provides a high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, a radio access network known as an evolved universal terrestrial radio access network (E-UTRAN) includes multiple evolved Node-Bs (eNBs) for communicating with multiple user equipments (UEs), and for communicating with a core network including a mobility management entity (MME), a serving gateway, etc., for Non-Access Stratum (NAS) control.
A LTE-advanced (LTE-A) system, as its name implies, is an evolution of the LTE system. The LTE-A system targets faster switching between power states, improves performance at the coverage edge of an eNB, and includes advanced techniques, such as carrier aggregation (CA), coordinated multipoint (CoMP) transmission/reception, uplink (UL) multiple-input multiple-output (MIMO), etc. For a UE and an eNB to communicate with each other in the LTE-A system, the UE and the eNB must support standards developed for the LTE-A system, such as the 3GPP Rel-10 standard or later versions.
In addition, multiple cells (e.g., femto cells, pico cells) may be grouped into a cell cluster to improve quality of transmissions and/or receptions occurred in a coverage area of the cell cluster. However, a coverage area of a clustered cell is usually smaller than a coverage area of a macro cell. For example, a diameter of the coverage area of the clustered cell may be 50 m˜100 m. The UE may move across boundaries of the clustered cells, even if the UE moves with a moderate speed. Accordingly, the UE may need to perform handovers frequently, and performance improvement obtained from the cell cluster is decreased due to the frequent handovers.
Thus, how to reduce a number of the handovers performed by the UE is an important problem to be solved.